1. Field of the Invention
The present invention relates to fuel injection systems for gaseous fuel engines. In particular, the invention relates to a system by which a compressed natural gas fueled engine can obtain efficiencies at or above those obtained by diesel engines.
2. Description of Related Art
Jensen U.S. Pat. No. 4,865,001 discloses a gaseous fuel injector valve, having a tubular body and stemmed poppet valve, for injection of a mixture of a gaseous and a liquid fuel into a diesel engine. The poppet valve includes a coil compression spring which normally urges the valve stem into a closed position sealing a fuel flow passage into the combustion chamber and has an outwardly opening valve face portion over which the outflowing supply of fuel passes. The injector valve is electronically controlled by a solenoid valve to cause gaseous fuel to be admitted into engine cylinder during the part of the compression stroke after the exhaust valve has closed and prior to rapid increase in the compression pressure that follows. However, this injector is not designed for use in engines that operate solely with gaseous fuels, nor does it deal with the problems associated with engines that are operated solely using gaseous fuels, and particularly, the need to obtained increased efficiency or the difficulties of igniting a gaseous fuel (the liquid fuel serves as a pilot for ignition of the gaseous fuel, being injected after the gaseous fuel).
In U.S. Pat. No. 4,505,249 of Young, a fuel control system for gaseous fueled engines is disclosed wherein a pressure regulator is provided for maintaining a constant pressure from the fuel source. However, Young's system is a carburetion system and is primarily directed to using the gaseous fuel in supplementing the fuel supply of a diesel engine. Thus, the Young patent, also does not deal with the problem increasing the efficiency of an engine fueled solely with compressed gas; carburetor-type compressed gas systems, which work like a conventional gasoline engine, have a lower efficiency than a diesel engine.
Lewis et al. disclose in U.S. Pat. No. 4,430,978, a system for the direct injection of liquid petroleum gas in to an engine. The Lewis et al. system compensates for the effect of variations in fuel pressure and density on the fuel metering accuracy by measuring the pressure differential across the fuel injector and varying the duty cycle (pulse width) of the injector to compensate for supply pressure variations. Furthermore, since the Lewis et al. system injects liquid gas, compensation must be provided for the vaporization of liquid gas fuel in the system upstream of the injector and in the injector itself.
Of course, numerous systems are known by which an engine may be operated solely with compressed gas as a fuel; see, for example, Dolderer U.S. Pat. No. 4,774,909, Reggiani U.S. Pat. No. 4,632,083, and Pagdin U.S. Pat. No. 4,617,904. Dolderer recognizes the problem that gas engines have been unable to match the efficiency of diesel engines and the difficulties that have been encountered in trying to do so, and like the Lewis et al. system, Dolderer injects gas fuel in a liquid state. No prior art device has successfully addressed the problems associated with the injection of gaseous fuels, into an engine, in a gaseous state and as the only fuel, so as to achieve efficiencies at or above those attainable by a conventional diesel engine.